1. Field of the Invention
The invention relates to electrical energy management systems that shed and restore prioritized electrical controlled loads in such a manner as to have minimum impact on the lifestyle of residential occupants and yet to maximize utility company revenue by keeping power consumption close to a level that utilizes all of the utility company's capacity to generate electrical power from hydroelectric, nuclear, coal-fired and other generating sources that have relatively low operating costs but require very large capitol outlays to construct, thereby avoiding the need for the utility company to use oil-powered peak load generating sources that sharply increase the rates that must be charged to utility customers.
The copending patent application "SYSTEM AND METHOD FOR OPTIMIZING SHED/RESTORE OPERATIONS FOR ELECTRICAL LOADS", by Hedges et al., filed on Sept. 26, 1980, now U.S. Pat. No. 4,324,987, assigned to the present assignee, and incorporated herein by reference, provides a detailed disclosure of a computerized residential energy controller that makes power shed and restore decisions of prioritized controlled loads on the basis of substantially instantaneous measurements of the total power being delivered to the residence. Although test data obtained show that the residential energy controller maintains total energy consumption of a residence below a preselected power limit selected by the residence owner, and can usually accomplish this desirable result without serious negative impact on the lifestyle of the occupants of the residence, the average power consumption of the residence is always at a significant amount below the preselected demand limit because the instantaneous power consumption is never allowed to exceed the preselected demand level without causing a decision to shed at least one load. Thus, the power delivered to the residence controlled by the power shed-restore device of the Hedges et al. application is always less than or equal to the preselected power limit, and the average power therefore is less than the preselected power limit. Consequently, utility revenues are reduced more than is desirable, and since less energy is consumed by the residents during peak energy requirement hours, the impact on the lifestyle of the occupants is ordinarily greater than would be desired.
It has been found that energy controllers that make shed and restore decisions based on instantaneous power measurements result in an excessive number of switching operations to turn controlled loads on and off under certain operating circumstances. This can result in faulty operation and reduced reliability and useful life of many appliances and electrical loads that are commonly found in residences.
Another problem that has been determined to exist for prior residential energy controllers is that undesirable "cycling" sometimes occurs, wherein the system will automatically first shed a number of loads, then recognize within a short time that too many loads were shed, and then restore too many loads, and so forth.
It is an object of the invention to provide an electrical energy controller for shedding and restoring loads to an establishment or residence to provide maximum use of energy up to a preselected demand limit with more accuracy than is possible with prior art energy shedding and restoring devices.
It is another object of the invention to provide an electrical energy shedding and restoring system that provides maximum energy utilization up to a selected demand limit, with minimum impact on the lifestyle of an occupant of a residence, and with a minimum number of load switching operations.
It is another object of the invention to provide a power shed-restore system that avoids rapid "load cycling" that occurs for some prior art power shedding and restoring devices.